1. Field of the Invention
This invention is a device for biasing a field effect transistor in an optimal manner for both small and large signal operation. While this circuit can be used for any FET, it is especially attractive for GaAs FET's used as microwave power amplifiers.
2. Description of the Prior Art
A prior art search has uncovered the following references:
U.S. Pat. No. 4,011,518 is a microwave GaAs FET amplifier with a temperature compensating bias to minimize intermodulation distortion. The bias varies only with temperature. No provision is made to compensate for variations in the input signal strength as in the present invention.
U.S. Pat. No. 4,077,013 is an audio power amplifier with a switched bias supply to minimize power consumption. This invention activates the bias current of a Darlington pair in the presence of an input signal. Neither the bias nor the impedance of the network is altered to accommodate for small and large signal operation as in the present invention.
U.S. Pat. No. 4,123,722 is an operational amplifier decoupling circuit which uses a matched amplifier to compensate for voltage offsets and leakage currents of the amplifier. It is not intended as a bias source nor does it in any way adapt for small and large signal operation as does the present invention.
U.S. Pat. No. 4,152,666 is a FET amplifier which uses a circulator to isolate the input signal and supply a fixed bias to the gate. The bias is not active nor does it adjust in any way for large and small signal operation as does the present invention.
The prior art search also uncovered the following secondary references:
U.S. Pat. Nos. 4,105,944, 3,501,710, 4,042,886, 3,906,386, and 3,747,005.